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Results from Borexino

Results from Borexino. NOW 2012 September 9-16, 2012. Davide Franco CNRS-APC. Detector layout and radiopurity. Stainless Steel Sphere: 2212 PMTs 1350 m 3. Scintillator: 270 t PC+PPO in a 150 m m thick nylon vessel. Water Tank: g and n shield m water Č detector

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Results from Borexino

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  1. Results from Borexino NOW 2012 September 9-16, 2012 Davide Franco CNRS-APC

  2. Detector layout and radiopurity Stainless Steel Sphere: 2212 PMTs 1350 m3 Scintillator: 270 t PC+PPO in a 150 mm thick nylon vessel Water Tank: g and n shield m water Č detector 208 PMTs in water 2100 m3 Nylon vessels: Inner: 4.25 m Outer: 5.50 m Carbon steel plates

  3. Borexino detects solar n via their elastic scattering off electrons in a volume of highly purifiedliquid scintillator Mono-energetic 0.862 MeV 7Be neutrinos: main target Mono-energetic 8B, pep, CNO and possibly pp neutrinos Detection via scintillation light: Very low energy threshold Good position reconstruction Good energy resolution BUT… No direction measurement The n induced events can’t be distinguished from other b events due to natural radioactivity Detection principles and n signature Extreme radio-purity of the scintillator is a must!

  4. Detector Calibration Detector response vs position: • 100 Hz 14C+222Rn in scintillator in >100 positions Quenching and energy scale: • Beta: 14C, 222Rn in scintillator • Alpha: 222Rn in scintillator • Gamma: 139Ce, 57Co, 60Co, 203Hg, 65Zn, 40K, 85Sr, 54Mn • Neutron: AmBe MC-G4Bx Data May 2007 Pulse shape of 14C events LY ~ 500 p.e./MeV Ph.Y. ~ 12000 photons/MeV Data - MC

  5. 7Be neutrino (862 keV) rate @ 4.6%Phys. Rev. Lett. 107, (2011) 141302 740 live days Systematics MC Fit Analytical Fit

  6. Implication of the 7Be measurement Pee = 0.51 ± 0.07 @ 867 keV no power to resolve low/high metallicity problem • No oscillation excluded @ 5.0 s • Assuming MSW-LMA: • f7Be= 0.97± 0.09 • fpp = 1.013 +0.003 -0.010 • fCNO < 1.7% (95 % C.L.) Neutrino magnetic moment limit: mn < 5.4 10-11 mb

  7. The Day-Night Asymmetry A neutrino “regeneration” is expected only in the LOW solution LOW ruled out at 8.5 s Adn = 0.001 ± 0.012 (stat) ± 0.007 (syst)

  8. 8B neutrinos with the lowest threshold: 3 MeV Expected 8B n rate in 100 tons of liquid scintillator above 2.8 MeV: 0.26±0.03 c/d/100 tons 2.6 MeV g’s from 208Tl on PMT’s and in the buffer All volume R < 3 m (100 tons) Energy spectrum in Borexino (after m subtraction) live-time: 246 days S/B ratio < 1/6000!!! > 5s distant from the 2.6 MeV g peak

  9. raw spectrum m cut FV cut cosmogenic, neutron, 214Bi and 10C cuts 208Tl 8B neutrino rate measurement

  10. First observation of pep neutrinos m + 12C → m + 11C + n 11C t ~ 30 min + p → d + g →11B + e++ ne Three Fold Coincidence (TFC): space-time veto removes 90% of 11C paid with 50% loss of exposure

  11. o-Ps in scintillators D. Franco, G. Consolati, D. Trezzi, Phys. Rev. C83 (2011) 015504 • ~ 3 ns • p ~ 50% Measurements of the o-Ps mean-life and formation probability in scintillators with the PALS technique Pulse shape induced distortion MC

  12. Multivariate maximum likelihood fit Pulse shape test Energy spectral fit Pulse shape fit Radial fit

  13. Δχ2 profile for fixed pep and CNO rates Borexino limit pep neutrinos: results • pep neutrinos: • Rate: 3.1 ± 0.6(stat) ± 0.3(sys) cpd/100 t • Assuming MSW-LMA: Φpep = 1.6 ± 0.3 108 cm-2 s-1 • No oscillations excluded at 97% C.L. • Absence of pep solar ν excluded at 98% CNO neutrinos: • only limits, correlation with 210Bi; • CNO limit obtained assuming pep @ SSM • CNO rate < 7.1 cpd/100 t (95% c.l.) • Assuming MSW-LMA: • ΦCNO < 7.7 108 cm-2 s-1 (95% C.L.) • the strongest limit to date • not sufficient to resolve metallicity problem

  14. The Borexino Solar neutrino spectroscopy

  15. Status and future perspectives • Since July 2010, purification campaigns: • Nitrogen stripping successful in 85Kr removal: • 85Kr < 8.8 cpd / 100 t (2007-2010: 31.2 ± 5) • moderate success in 210Bi removal by water extraction: • 210Bi : (16 + 4) cpd / 100 t (2007-2010: 41.0 ± 2.8) • unprecedented 238U and 232Th radio-purity: • 238U < 9.7 10-19 g/g and 232Th < 2.9 10-18 g/g • 210Po natural decreasing: • ~5 cpd / t • Borexino phase II started: • Solar neutrino program: • - Improve 7Be, 8B → test of MSW • - Confirm pep at more than 3 σ • - Improve upper limit on CNO → probe metallicity • Attempt direct pp measurement • more statistics for an update of geo-neutrino measurement; • another long-term scientific goals under discussion (sterile?)

  16. A glance at the Borexino physics results Neutrino speed: Measurement of CNGS muon neutrino speed with Borexino, submitted Pep & CNO limit : First evidence of pep solar neutrinos by direct detection in Borexino, Phys. Rev. Lett. 108 (2012) 051302. 7Be ADN:Absence of day--night asymmetry of 862 keV 7Be solar neutrino rate in Borexino and MSW oscillation parameters, Phys. Lett. B 707 (2012) 22. 7Be @ 5%:Precision measurement of the 7Be solar neutrino interaction rate in Borexino, Phys. Rev. Lett. 107 (2011) 141302. Solar antinu limits:Study of Solar and other unknown anti-neutrino fluxes with Borexino at LNGS, Phys. Lett. B696 (2011) 191-196. Geo-nu: Observation of Geo-Neutrinos, Phys.Lett. B687 (2010) 299-304. 8B > 3 MeV: Measurement of the solar 8B neutrino rate with a liquid scintillator target and 3 MeV energy threshold in the Borexino detector, Phys. Rev. D82 (2010) 033006. 7Be @ 10%: Direct Measurement of the Be-7 Solar Neutrino Flux with 192 Days of Borexino Data, Phys. Rev. Lett. 101 (2008) 091302. 7Be @ 17%: First real time detection of Be-7 solar neutrinos by Borexino, Phys. Lett. B658 (2008) 101-108 + muon modulation + cosmogenics + axions + Pauli principle + magnetic moment + ….

  17. Milano Perugia Borexino Collaboration Genova Princeton University APC Paris Virginia Tech. University Munich (Germany) Dubna JINR (Russia) Kurchatov Institute (Russia) Jagiellonian U. Cracow (Poland) Heidelberg (Germany)

  18. Backup

  19. Geo-neutrinos: results Null hypothesis rejected at 4.2s

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